Later in life, I learned that the sports I liked were individual sports that absolutely did not involve reacting to (or working with) other people (which, for whatever reason, I'm really bad at).

My personal favorite sport is cycling. It's just me and the road, and getting better is beating personal bests (rather than beating other people). I'd lump swimming and running into that same category, but YMMV.

So sorry to hear he's going through such a rough spot! If it's any consolation to him, this is from a guy who was always picked last in gym class: it gets better.